The present invention relates to a method for making a powder coating.
The powder coating is usually produced by passing it through the following processes in sequence: 1) a process for premixing materials for coating under dry conditions, 2) a process for melting and kneading the materials, 3) a process for pulverizing it, and 4) a process for classifying it.
The performance of a coated film made by using a powder coating, in particular, the presence or absence of uneven irregularities on the coated film as well as the gloss, is affected by the average particle diameter and particle size distribution range of the powder coating particles. That is, as the average particle diameter becomes smaller and/or the particle size distribution range becomes narrower, the surface smoothness becomes better. As a result, the irregularities on the coated film disappear and the gloss is improved.
To make the average particle diameter of a powder coating smaller, it is preferable to pulverize the powder coating finer. But the average particle diameter is from about 20 to 30 .mu.m using conventional procedures, such as, for example pulverizing particles by a hammer mill.
To make the particle size distribution range narrower, it is preferable to classify the powder coating. But there occurs a problem that the efficiency of making a powder coating decreases greatly due to this classification.